The Southern Ocean GLOBEC broad-scale survey work aboard the R/V
N.B. Palmer was completed on 20 May with conclusion of work at Station
# 84. Since the last report, work has been completed at consecutive stations
68 to 88. Through the 23rd of May, the work has included eighty-six CTD
profiles, one hundred nine XBTs, twenty-one XCTDs, 40 FRRF deployments
on the CTD, eighteen 1-m2 MOCNESS tows, sixteen surface ring
net tows, sixty-three sonabuoy and five satellite tracked drogue deployments,
five ROV under ice deployments, bird and mammal surveys on most of the
transits between stations, BIOMAPER II towyo's between a majority of the
stations. In addition, more than one hundred four short term incubations
for determination of gross photosynthesis rates and a large number of water
bottle samples for microzooplankton determination and other biological
constituents have been processed. Seabeam bathymetry data, ADCP data, surface
temperature, salinity, and fluorescence data, and meteorological data continue
to be collected around the clock.
The physical data now in hand, indicate that the strong intrusion of Upper Circumpolar Deep Water (UDCW) on the west Antarctic Peninsula continental shelf that aligns along the axis of the canyon that extends from the shelf break into Marguerite Bay is driving water out of the Bay to the southwest. The distribution of the temperature maximum below 200 m for the completed survey grid shows that the coastal current flowing outward from the southern portion of Marguerite Bay turns and flows in a southwesterly direction along the west Antarctic Peninsula continental shelf. It appears that the southwesterly flow out of Marguerite Bay turns into the embayment between Rothschild and Charcot Island and then flows back out around Charcot Island. The southwesterly flowing current appears to be continuous around the western tip of Charcot Island and southward as far as the Wilkins Ice Shelf. The ADCP current patterns at the surface and deeper are consistent with the flow patterns suggested by the maximum temperature distribution. The ADCP-derived current patterns show south-southwesterly flow along the western side of Charcot Island. The current vectors also show the southwesterly current along the inner shelf inside of survey transects eleven, twelve, and thirteen (the last three lines in the grid). The current vectors indicate that flows associated with the coastal current are on the order of 5-8 cm/sec. Several satellite drifters deployed in the Bay have been entrained in the coastal current flow and on several occasions have rocketed along to the southwest at speeds up to 40 cm/sec.
The open waters of the continental shelf within the survey grid remain largely ice free, although the meteorological conditions are such that the heat flux out of the ocean will soon bring the surface waters to the freezing point. The embayments in which the R/V Palmer has been located during the past several days in search of top predators (birds, especially penguins, and whales) are full of unconsolidated brash ice (and icebergs), which is about to solidify.
Sea bird distributions and abundance patterns are in line with previous studies in this region and show lower abundances of sea birds offshore and a switch in the dominant birds present in the different hydrographic and biological regimes. Offshore, several different bird species were most abundant in the counts from one transect section to the next (i.e., Blue Petrel, Cape Petrel, Antarctic Petrel, and Southern Fulmar), whereas inshore in the coastal water, the Snow Petrels were usually dominant. Whales occurred variably during the latter half of the broad-scale survey with humpbacks and minkes being observed most often near the coast. The passive listening to marine mammal vocalizations through use of sonabuoys provided a number of songs of humpbacks and other sounds (grunts and moans) that were probably from minke whales and seals.
The completion of the survey grid provided additional evidence that the pattern of high acoustic backscattering from the coast to near the outer margin of the continental shelf and then much lower backscattering in the offshore waters is continuous through the entire survey region. The scattering intensities along the most southerly sections were generally lower than in the region just south of Marguerite Bay. VPR and MOCNESS data showed that this area was dominated by copepods, especially below 100 m, and fewer krill were observed.
The technical support we are receiving from the Raytheon technical support group and the ship's officers and crew continues to be excellent. To read the daily reports, which provide more detail about our work to date, go to the U.S. GLOBEC Web site (www.usglobec.org) and click on the SO GLOBEC icon to get to the SO GLOBEC Web site.
Kindest regards, Peter Wiebe, Chief Scientist